Question

Both UDP and TCP use port numbers to identify the destination entity when delivering a message. Give two reasons why these protocols invented a new abstract ID (port numbers), instead of using process IDs, which already existed when these protocols Were designed.

Short answer

Port numbers provide abstraction from process IDs and facilitate connection multiplexing.

Step-by-step solution

Introduction to Process IDs and Port Numbers

In computer systems, each running process is assigned a unique identifier known as a process ID (PID). This helps the operating system manage and address processes. Concurrently, both TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) use port numbers, which are abstract identifiers to route data to the correct application endpoint within a system.

Port Numbers Decouple Network and Process

One reason for using port numbers instead of process IDs is to create a layer of abstraction that separates network addressing from process IDs. This allows applications to listen for network traffic on specific ports independently of the internal process management by the OS. By using port numbers, the same application can listen on the same port regardless of its PID, making network communications more flexible and consistent.

Port Numbers Facilitate Application Multiplexing

Another reason is that port numbers facilitate the multiplexing of connections, allowing multiple network connections to be managed by a single process. Without port numbers, each connection might need its own process, which can be inefficient and cumbersome. Port numbers allow a single process to handle traffic from multiple connections by distinguishing the connections through different port numbers.

Key concepts

Process IDs

In computer systems, each process running on an operating system is assigned a unique identifier known as a Process ID (PID). This PID serves as a distinct fingerprint for each process, allowing the operating system to track and manage these processes efficiently. Think of PIDs as unique tags for every running application or service, helping ensure that resources are allocated correctly and preventing conflicts between processes.
However, while process IDs are key for managing these operations within a computer, they were not designed to handle network communication tasks. As a result, TCP and UDP use a different mechanism, namely port numbers, to facilitate the delivery of data over networks.

• PIDs keep track of applications within the OS.
• They are unique to each process.
• Useful for OS-level resource management.

Transmission Control Protocol (TCP)

Transmission Control Protocol (TCP) is one of the core protocols of the Internet Protocol Suite. TCP is designed to provide reliable, ordered, and error-checked delivery of a stream of bytes between applications running on hosts in a network. This reliability is crucial for applications where data integrity and order are important, such as email, web browsing, and file transfers.
TCP uses a process known as the "three-way handshake" to establish a connection before any data is transmitted. This process involves sending three signal packets between the sender and receiver to set up the communication link.

• Ensures reliable data transmission.
• Uses a three-way handshake for connection setup.
• Handles ordering and error-checking of data packets.

User Datagram Protocol (UDP)

User Datagram Protocol (UDP) is another key protocol within the Internet Protocol Suite. Unlike TCP, UDP opts for simplicity and speed over reliability. It does not perform error checking or ensure that packets arrive in order, making it suitable for applications that prioritize speed, like video streaming or online gaming.
Due to its design, UDP is often used where real-time performance is more critical than a perfect data transmission. This means that if some packets are lost during transmission, the application can still function smoothly without noticeable delays.

• Favors speed over reliability.
• Does not guarantee packet order or error-checking.
• Ideal for real-time applications like streaming.

Application Multiplexing

Application Multiplexing is the process by which multiple network communications are handled simultaneously by a single application. Port numbers play a central role in multiplexing by allowing a single process to manage multiple incoming or outgoing connections.
When data arrives at a system, port numbers guide it to the correct application endpoint. This means a single application can listen to different connections from different clients, as each client may connect through a different port number.
Moreover, multiplexing helps in efficiently using networking resources, allowing systems to handle more connections with less computational overhead.

• Makes single application management of multiple connections possible.
• Enables efficient use of networking resources.
• Facilitates functionality by allowing different sessions to occur simultaneously.